Low-lying Electric Dipole Strength Research Articles

Systematic study of the low-lying electric dipole strength in Sn isotopes and its astrophysical implications

Systematic study of the low-lying electric dipole strength in Sn isotopes and its astrophysical implications

Photo scattering and absorption cross section in framework of the sdfp-interacting boson model

Low-lying electric dipole strength is an interesting nuclear structure phenomenon which various collective models were employed in order to account for the observed properties of the photoresponse in nuclei. To determine general characteristics of the low-lying dipole strength it is reasonable to use the sdfp-interacting boson model (sdfp-IBM). Dipole strength, photo scattering and absorption cross section of the even–even Z=54 isotopes are calculated in the sdfp-IBM based on dual pairing of affine SU(1,1) Lie algebra and Bethe-ansatz equations. E1 excitations to the spin 1 member of the two-phonon quintuplet excitations (2+⊗3−) are also discussed with respect to the critical point symmetry E(5) in even–even Xe isotopes. SU(1,1) Lie algebra calculations were performed for each dipole using the sdfp-IBM, and the results are compared to the experimental data. The calculations confirm a good agreement for the fragmentation of the E1 strength.

Mean-field analysis of ground-state and low-lying electric dipole strength inC22

Properties of neutron-rich $^{22}$C are studied using the mean-field approach with Skyrme energy density functionals. Its weak binding and large total reaction cross section, which are suggested by recent experiments, are simulated by modifying the central part of Skyrme potential. Calculating $E1$ strength distribution by using the random-phase approximation, we investigate developments of low-lying electric dipole ($E1$) strength and a contribution of core excitations of $^{20}$C. As the neutron Fermi level approaches the zero energy threshold ($\varepsilon_F >\sim -1$ MeV), we find that the low-lying $E1$ strength exceeds the energy-weighted cluster sum rule, which indicates an importance of the core excitations with the $1d_{5/2}$ orbit.

Experimental results on the Pygmy Dipole Resonance

The so-called Pygmy Dipole Resonance, an additional structure of low-lying electric dipole strength, has attracted strong interest in the last years. Different experimental approaches have been used in the last decade in order to investigate this new interesting nuclear excitation mode. In this contribution an overview on the available experimental data is given.

Pygmy dipole resonance in stable Ca isotopes

The properties of the low-lying electric dipole strength in the stable 40 Ca, 44 Ca and 48 Ca isotopes have been calculated within the Extended Theory of Finite Fermi Systems (ETFFS). This approach is based on the random phase approximation (RPA) and includes the single-particle continuum as well as the coupling to low-lying collective states which are considered in a consistent microscopic way. For 44 Ca we also include pairing correlations. A good agreement with the existing experimental data for the gross properties of the low-lying strength has been obtained. We conclude that for the detailed understanding of the low-lying dipole strength an approach like the present one is absolutely necessary.

Direct reactions with exotic nuclei, nuclear structure and astrophysics

Intermediate energy Coulomb excitation and dissociation is a useful tool for nuclear structure and astrophysics studies. Low-lying strength in nuclei far from stability was discovered by this method. The effective range theory for low-lying strength in one-neutron halo nuclei is summarized and extended to two-neutron halo nuclei. This is of special interest in view of recent rather accurate experimental results on the low-lying electric dipole strength in 11Li. Another indirect approach to nuclear astrophysics is the Trojan-horse method. It is pointed out that it is a suitable tool to investigate subthreshold resonances.